U.S. patent number 4,956,715 [Application Number 07/409,283] was granted by the patent office on 1990-09-11 for image sensing device having a photometric element for setting an exposure condition for the image sensing device.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Nobuaki Date, Tadashi Okino, Syuichiro Saito, Nobuo Tezuka.
United States Patent |
4,956,715 |
Okino , et al. |
September 11, 1990 |
Image sensing device having a photometric element for setting an
exposure condition for the image sensing device
Abstract
An image sensing device includes an image sensor; a photometric
element which is arranged separate from the image sensor to measure
light with a diaphragm aperture fully opened; a storing time
control circuit arranged to variably control the storing time of
the image sensor; a circuit arranged to form exposure control
information from the output of the image sensor on the basis of the
output of the photometric element at least under a condition in
which the storing time is controlled by the storing time control
circuit; and an exposure control circuit arranged to control the
exposed condition of the image sensor on the basis of the exposure
control information.
Inventors: |
Okino; Tadashi (Kanagawa,
JP), Date; Nobuaki (Kanagawa, JP), Tezuka;
Nobuo (Kanagawa, JP), Saito; Syuichiro (Kanagawa,
JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
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Family
ID: |
13779107 |
Appl.
No.: |
07/409,283 |
Filed: |
September 19, 1989 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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169074 |
Mar 16, 1988 |
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726097 |
Apr 23, 1985 |
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Foreign Application Priority Data
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Apr 24, 1984 [JP] |
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59-82605 |
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Current U.S.
Class: |
348/230.1;
348/341; 348/344; 348/E3.019; 348/E5.035; 348/E5.036;
348/E5.037 |
Current CPC
Class: |
H04N
5/2351 (20130101); H04N 5/353 (20130101); H04N
5/2353 (20130101); H04N 5/2352 (20130101) |
Current International
Class: |
H04N
5/235 (20060101); H04N 3/15 (20060101); H04N
003/19 () |
Field of
Search: |
;358/909,228,213.13
;354/431,432,402 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brinich; Stephen
Attorney, Agent or Firm: Toren, McGeady & Associates
Parent Case Text
This is a continuation application of Ser. No. 07/169,074, filed
Mar. 16, 1988 now abandoned, which in turn is a continuation
application of Ser. No. 06/726,097 now abandoned, filed Apr. 23,
1985.
Claims
What is claimed is:
1. An image sensing device comprising:
(a) image sensing means;
(b) a photometric element;
(c) accumulating time control means for variably controlling the
storing time of said image sensing means;
(d) exposure information forming means for forming first exposure
control information based on an output of said photometric element,
and for forming second exposure control information based on an
output of said image sensing means, under a condition in which the
accumulating time is controlled by said accumulating time control
means; and
(e) exposure control means for correcting the exposure condition of
said image sensing means on the basis of said second exposure
control information, said exposure control means having a lower
responsiveness than said accumulating time control means.
2. A device according to claim 1, wherein said accumulating time
control means is provided to control the accumulating time by
clearing an image sensing signal in said image sensing means at a
predetermined timing.
3. A device according to claim 1, said exposure control means
comprising stop means for controlling the quantity of light
incident upon said image sensing means.
4. A device according to claim 3, wherein said photometric element
is disposed behind said stop means.
5. A device according to claim 1, said exposure control means
comprising shutter means for variably controlling the incident time
of light incident on said image sensing means.
6. A device according to claim 5, wherein said light incident time
controlled by said shutter means nearly corresponds to said
accumulating time.
7. An image sensing device according to claim 1, and further
comprising recording means for recording an output of said image
sensing means which is formed under a condition in which said
exposure control means corrects the exposure condition of said
image sensing means.
8. An exposure controlling method for a still video camera
comprising:
(a) a first step of forming first exposure control information for
an object to be photographed, said information being formed based
on light measuring means which is provided in addition to image
sensing means;
(b) a second step of controlling an aperture value of an iris based
on said first exposure control information, under a condition in
which the accumulating time of said image sensing means is also
controlled based on said first exposure control information;
(c) a third step of forming second exposure control information for
correcting said first exposure information based on an image
sensing signal formed by said image sensing means at said second
step; and
(d) a fourth step of controlling the level of subsequent image
sensing signals formed by said image sensing means based on the
second exposure control information formed at the second step.
9. A method according to claim 8, wherein, at said fourth step, the
quantity of light incident upon said image sensing means is
controlled on the basis of said corrected first exposure control
information.
10. A method according to claim 8, wherein, at said fourth step, at
least the incident time of the light incident upon said image
sensing means is controlled based on said corrected first exposure
control information.
11. An exposure controlling method according to claim 8, and
further comprising a step of recording and image sensing signal
formed by said image sensing means during said fourth step.
12. An image sensing device for a still video camera
comprising:
(a) stop means for controlling the quantity of light incident;
(b) image sensing means for forming an image sensing signal from
light incident through said stop means;
(c) light measuring means other than said image sensing means for
detecting the luminance of an object to be photographed;
(d) accumulating time control means for controlling the
accumulating time of said image sensing means;
(e) control means for controlling said stop means;
(f) exposure control information forming means for forming light
metering information based on said image sensing signal, under a
condition in which the accumulating time is controlled by said
accumulating time control means, and in which said stop means is
controlled by said control means according to an output of said
light measuring means; and
(g) level control means for controlling the level of subsequent
image sensing signal formed in said image means according to said
light metering information.
13. An image sensing device according to claim 12, said exposure
control means comprising correcting means for correcting said stop
means on the basis of said light metering information.
14. An image sensing device according to claim 12, and further
comprising recording means for recording an image sensing signal
which is level controlled by said level control means.
15. An image sensing device for a still video camera,
comprising:
(a) image sensing means for generating an image signal; and
(b) exposure control means for controlling light incident to said
image sensing means, comprising:
(1) a shutter member located in front of said image sensing
means;
(2) presetting means for presetting an exposure time of said
shutter member; and
(3) control means for accumulating the image signal in the image
sensing means for a period of time corresponding to the exposure
time preset by said presetting means, and for correcting said
preset exposure time based on said image signal, and for
controlling said shutter member so as to subsequently expose said
image sensing means for said corrected preset exposure time.
16. A device according to claim 15, wherein said shutter member
includes a shutter blade.
17. A device according to claim 15, wherein said presetting means
includes manual setting means.
18. A device according to claim 15, wherein said presetting means
further includes light metering means, and controls said exposure
time by using a light metering information of said light metering
means.
19. A device according to claim 15, wherein said exposure control
means further includes a diaphragm.
20. A device according to claim 19, which further comprises
recording means for recording the image signal whose exposure time
is controlled by the control means.
21. An image sensing and recording device for a still video camera,
comprising:
(a) image sensing means for generating an image signal and having
variable accumulating time;
(b) a trigger member;
(c) a diaphragm for adjusting an amount of light incident on said
image sensing means;
(d) a shutter located in front of said image sensing means which
controls a time of incidence of light on said image sensing
means;
(e) indication means for indicating a time value for the light
incidence by said shutter and an aperture value for said
diaphragm;
(f) control means for setting said diaphragm to the aperture value
corresponding to the indication of said indication means by an
operation of said trigger member, and for driving said image
sensing means instead of said shutter to store the image signal for
the time indication by said indication means to obtain a first
image signal;
(g) shutter driving means for causing the light incidence, in
accordance to the first image signal, to form a second image signal
for said image sensing means for a predetermined shutter time;
and
(h) recording means for recording the second image signal as a
still image.
22. A device according to claim 21, wherein said setting means
includes manual setting means.
23. A device according to claim 21, wherein said presetting means
further includes light metering means, and controls said
predetermined time value based on a light metering information of
said light metering means.
24. An image sensing device for a still video camera,
comprising:
(a) image sensing means for generating an image signal, said image
sensing means variably controlling the accumulating time;
(b) a trigger member;
(c) a diaphragm for adjusting an amount of light incident on said
image sensing means;
(d) a shutter located in front of said image sensing means which
controls a time of incidence of light on said image sensing
means;
(e) control means for forming a first image signal in response to
said triggering means to drive said diaphragm and said image
sensing means to obtain a predetermined aperture value and a
predetermined accumulating time, respectively, then correcting said
predetermined accumulating time based on said first image signal
and successively forming a second image signal by driving said
shutter in accordance with the first image signal to effect
incidence of light on said image sensing means for a predetermined
time; and
(f) recording means for recording the second image signal.
25. A device according to claim 24, wherein the diaphragm maintains
a full-open state until said trigger member operates.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image sensing device which permits
highly accurate exposure control.
2. Description of the Prior Art
Heretofore, a device of this kind has been required to have an
extremely high exposure control accuracy in taking a still picture
of an object to be photographed since the response range of the
image sensor is extremely narrow. Meanwhile, where an optical view
finder of the TTL (through the lens) type is employed in the device
of this kind, the diaphragm aperture of the device is preferably
left in a full open state until immediately before photographing
for the purpose of having a bright image plane within the view
finder. Therefore, with the aperture in a full open state, light
measurement is performed by means of a photometric element which is
arranged separate from the image sensor and which has a wider
dynamic range than the image sensor; and exposure control is
performed on the basis of a photometric data thus obtained, so that
exposure control can be quickly carried out after the start of
photographing.
However, the photometric information thus obtained with the maximum
aperture differs from photometric information obtained with the
diaphragm aperture stopped down to a value used for actual
photographing. It has been ascertained that this discrepancy in the
photometric information is not ignorable in the case of an image
sensor of a narrow dynamic range.
Furthermore, to solve the problem of the error or discrepancy
between the photometic data obtained with the maximum aperture and
the photometric data obtained with an actual stopped down aperture,
it is conceivable to obtain accurate exposure data by driving the
diaphragm and a shutter to have their values actually used
immediately before an actual photo-taking operation. However, such
an arrangement results in an extremely poor response which often
causes the photographer to miss a desired shutter opportunity.
This invention is directed to the solution of the problems
presented by the prior art devices. It is, therefore, an object of
this invention to provide an image sensing device and an exposure
control method, wherein exposure control may be accomplished with a
high degree of accuracy by operating an image sensor under
substantially the same exposure condition as the condition under
which photographing is to be performed with the length of
preparation time required for photographing shortened to a minimal
time.
The above and further objects and features of this invention will
become apparent from the following detailed description of a
preferred embodiment thereof taken in conjunction with the
accompanying drawings.
Summary of the Invention
To attain the object of the invention, an embodiment of this
invention is arranged to obtain a first exposure control
information by means of a photo-sensitive element which is separate
from an image sensor while the storing time of the image sensor is
under control; the exposure of the image sensor is controlled on
the basis of the first exposure control information; and a second
exposure control information is formed from an image sensing signal
thus obtained. Therefore, although the diaphragm aperture is held
in a full open state for an optical view finder before photography,
a still picture recording can be promptly carried out and the
exposure condition can be simply, quickly and accurately
performed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view showing the structural arrangement of an
image sensing device in an embodiment of this invention.
FIG. 2A is a circuit diagram showing the electric circuit blocks of
the embodiment shown in FIG. 1.
FIG. 2B is an illustration showing, by way of example, an image
sensor.
FIG. 3 is a timing chart.
FIGS. 4A-4D are illustrations showing the image sensor in relation
to shutter blades.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:
FIG. 1 shows, in a sectional view, the mechanical arrangement of an
image sensing device embodying this invention. The illustration
includes a turnable mirror 21; an image sensor 22 such as a CCD;
and a photometric element 23 such as a silicon photo-cell (SPC)
having corrected spectral luminous efficacy. When the mirror 21 is
in a lowered position 21a, the optical path of the device is as
follows: A light flux, which has passed through a photo-taking lens
24 and a diaphragm aperture 25, is imaged on a focusing glass 26 by
the mirror 21. The optical image thus obtained passes through a
half-mirror 27, a pentagonal prism 20 and an eye piece 28 to permit
visual observation through a view finder part. Meanwhile, a portion
of the light flux reflected by the halfmirror 27 reaches to the
photometric element 23.
When the mirror 21 is in an up-lifted position 21b, 100 percent of
the light flux, which has passed through the photo-taking lens 24
and the aperture 25, reaches the image sensor 22, if it is not
blocked by a shutter 30. The shutter 30 is a focal plane shutter
consisting of blades S1 and S2, as will be further described later
herein.
FIG. 2A is a block diagram showing, by way of example, the
electrical circuit arrangement of the image sensing device
embodying this invention. The same reference numerals as those used
in FIG. 1 denote the same component elements. A signal processing
circuit 1 is arranged to perform various correcting operations on
luminance and chrominance components of a signal produced from the
image sensor 22. Reference numerals 2 and 3, respectively, denote a
gate circuit and a recorder. The gate circuit 2 is arranged to have
the open period and the operation timing thereof controlled by a
control output X2 of a sequence controller 14. A driver circuit 4
is arranged to drive the image sensor 22. A clock pulse generator 5
is arranged to provide the driver circuit 4 with varied timing
signals and also to form a vertical synchronizing signal. A
diaphragm driving circuit 6 is arranged to control the operation
and the aperture value of the diaphragm in accordance with an
output X6 of the sequence controller 14 and the output of a
sample-and-hold circuit 10. A shutter driving circuit 7 is arranged
to control the operation and exposure time based on outputs X5 and
X'5 of the sequence controller 14 and the output of a shutter time
setting circuit 8. The shutter driving circuit 7 and the diaphragm
driving circuit 6 form exposure control means. The operation of the
shutter blades S1 and S2 is under the control of the outputs X5 and
X'5 of the sequence controller 14. The shutter time setting circuit
8 consists of a manually operated dial, etc., and is arranged to
designate a shutter time value Tv of the shutter 30. A computing
circuit 9 is arranged to produce aperture information values Av1
and Av2 by selectively computing the shutter time Tv and luminance
information Bv1 produced from the photometric element 23 or an
output Bv2 of an integration circuit 11. The sample-and-hold
circuit 10 serves as storage means for storing the computation
outputs Av1 and Av2 of the computing circuit 9 by sampling them at
a timing defined by a control output X1 of the sequence controller
14. The integration circuit 11 is arranged to form exposure control
information by integrating, for one vertical period, a luminance
signal which is suitably formed by the signal processing circuit 1.
A switch circuit 12 is arranged to selectively supply the output
Bv1 of the photometric element 23 or the output Bv2 of the
integration circuit 11 to the computing circuit 9. When a control
output X3 of the sequence controller 14 is at a low level, the
switch circuit 12 is connected to one side "a" thereof, and to
another side "b" when the output X3 is at a high level. A storing
time control circuit 13 is arranged to serve as storing time
control means and operates under the control of the sequence
controller 14. The storing time of the image sensor 22 is
controlled by the control circuit 13 with the pulses which are
supplied to the image sensor 22 controlled based on to the output
of the shutter time setting circuit 8.
The sequence controller 14 is arranged to receive the output of a
release circuit 15, which forms a release signal, and the output of
the clock pulse generator 5 which forms a synchronizing signal. The
controller 14 produces control outputs X1-X8 which are shown in
FIG. 3.
A mirror driving circuit 29 is arranged to control the position of
the mirror 21 in accordance with the output X8 of the sequence
controller 14.
FIG. 2B shows, by way of example, the details of the image sensor
22, which is a frame transfer type CCD in this specific embodiment.
Referring to FIG. 2B, the illustration includes a light receiving
part 16, a storage part 17, a horizontal shift register 18 and an
output amplifier 19. The image sensor 22 is provided with an
overflow drain OFD, which may be arranged in the same manner as the
one disclosed, for example, in Japanese Patent Publication No. SHO
51-22356. In other words, the overflow drain OFD is arranged via a
predetermined potential barrier between the vertical shift
registers which form the light receiving part 16.
Shift pulses .0.1 and .0.2 are arranged to vertically transfer the
electric charges of the light receiving part 16 and the storage
part 17. A shift pulse .0.3 is arranged to horizontally transfer
the electric charge which has been vertically transferred from the
storage part 17, one line of the storage part 17 at a time. Next,
the embodiment which is arranged as shown in FIGS. 2A and 2B
operates as described below with reference to FIGS. 3 and
4A-4D:
FIG. 3 is a timing chart. FIGS. 4A-4D show the image sensor 22 in
relation to the movement of the shutter blades S1 and S2, as viewed
from the side of the lens.
The release signal is at a low level when a power supply switch
(not shown) is off. Under this condition, the outputs X6 and X8 of
the sequence controller 14 are at low levels. With the output X6 at
the low level, the diaphragm driving circuit 6 causes the diaphragm
to be full open. With the output X8 at the low level, the mirror
driving circuit 29 has the mirror 21 in the lowered position 21a as
shown in FIG. 1. Furthermore , under this condition, the outputs X5
and X'5 are at low levels to have the blades S1 and S2 in left and
middle positions respectively, as shown in FIG. 4A. Accordingly,
the image sensor 22 is in a light shielded state with the shutter
blades S1, S2 in these positions.
When the power supply switch (not shown) is turned on, the
photometric computing circuit 9 begins to operate. The value Bv1 of
the light quantity incident on the photometric element 23 and the
shutter time value Tv, which is preset by means of a dial or the
like, are computed to obtain, through an APEX computation, the
aperture value Av1 which is necessary for obtaining an apposite
exposure condition. Furthermore, the aperture value Av continuously
varies based on the light quantity incident on the photometric
element 23 up to a point of time t1 at which time a release signal
is obtained from the release circuit 15.
Furthermore, after the power supply switch is turned on, the clock
pulse generator 5 produces a vertical synchronizing signal VD, etc.
The outputs of the generator 5 are supplied to the sequence
controller 14, etc. By this, the operations of the whole image
sensing device are synchronously controlled.
Then, the shift pulses .0.1 - .0.3 are supplied, as shown in FIG.
3, to have an image, which is formed at the image sensor 22, read
out based on to the standard television period. After that, when
the release switch, etc., are turned on at the point of time t1,
the release signal being formed at the release circuit 15. Then,
the outputs X6 and X8 become high levels. The output X1 also
becomes a high level. As a result, the sample-and-hold circuit 10
holds the aperture value Av obtained at the point of time t1. The
diaphragm driving circuit 6 then stops down the aperture of the
diaphragm 25 to bring the aperture to the value Av1, which is the
aperture value Av at that time. Furthermore, the mirror driving
circuit 29 causes the mirror 21 to move to the up-lifted position
21b of FIG. 1. Meanwhile, in response to the release signal, the
output X5 becomes a high level to cause the shutter blade S2 to
begin to move toward a right position as shown in FIG. 4B. When the
movement to the right position of the shutter blade S2 is completed
at a point of time t2, the image sensor 22 is no longer shielded
from light. With time having lapsed to another point of time t3,
the diaphragm aperture 25 completely reaches the aperture value Av1
and the mirror 21 is brought fully into the up-lifted state 216.
The output X4 becomes a high level at a point of time t4 in
synchronization with another vertical synchronizing signal VD
produced after the aperture control completion point of time t3.
After the point of time t4, the storing time control circuit 13
produces a pulse at a point of time t5 after the lapse of time
which corresponds to the shutter time value Tv set by the shutter
time setting circuit 8. Following this, the shift pulses .0.1 are
supplied in a greater number than the number of lines of the light
receiving part 16 and at a high speed.
By this, the electric charge within the light receiving part 16 is
collected in an area close to a border line between the light
receiving part 16 and the storage part 17. The collected electric
charge then overflows there and is discharged into the overflow
drain OFD. At that time, a several line portion of the overflowing
electric charge flows into the storage part 17. However, the amount
is negligible.
Therefore, the image information accumulated at the light receiving
part 16 during a period of time To from completion of vertical
transfer after the point of time t5 to a next vertical transfer
point of time t6 is produced from the output amplifier 19 during
one field period between the points of time t6 and t10, as shown in
FIG. 3. There is obtained the following relation:
To.congruent.V2.sup.Tv.
Furthermore, during this period, the integration circuit 11
performs integration for every field and is reset by the rise of
the signal VD.
Since the output X3 is at a high level during a period between the
points of time t6 and t10, the switch circuit 12 is shifted to the
side "b" thereof. The computing circuit 9 computes an integration
output Bv2, integrated during the period from the point of time t6
to the time point t10 to obtain the new aperture value Av2. The
sample-and-hold circuit 10 then holds this value Av2 when the level
of the output X1 becomes low at a point of time t9 immediately
before the point of time t9.
Accordingly, the diaphragm driving circuit 6 adjusts the value Av
of the diaphragm aperture to the value Av2. In other words, the
aperture is corrected by producing the aperture value Av2 obtained
at the point of time t10 in place of the aperture value Av1 which
is based on the light measurement (photometric) value Bv1 obtained
at the point of time t1.
According to the invention, extremely accurate exposure control
information can thus be obtained. It is another advantage that
accurate exposure control information is obtainable by a simple
arrangement without performing exposure control by actually driving
the shutter 30.
Furthermore, at a point of time t8 immediately after completion of
the vertical transfer between the time points t6 and t7, the level
of the output X5 becomes high to bring the shutter blade S1 into
the middle position, as shown in FIG. 4C.
Accordingly, the image sensor 22 is again shielded from light.
Therefore, no smearing takes place at this point of time. Next,
upon completion of vertical transfer between time points t10 and
t11, the level of the output X5 becomes low. The blade S1 begins
again to move toward the left position. An exposure thus begins.
Then, at a point of time t12 after the lapse of the period of time
To which corresponds to the shutter time value Tv set by the
shutter time setting circuit 8, the level of the output X'5 becomes
low to allow the shutter blade S2 to begin to move toward the
middle position thereof. In other words, as shown in FIG. 4D, the
shutter blade S2 begins to shield the image sensor 22 from light
delaying as much as the period of time To from the other shutter
blade S1. The exposure is thus carried out for the period of time
To. Furthermore, at a point of time t14, the levels of the outputs
X1, X6 and X8 become low. Therefore, the mirror 21 resumes the
lowered position 21a. The diaphragm aperture returns to a full open
state.
The image sensor 22 is still shielded from light during vertical
transfer during a period between the time points t13 and t14.
Therefore, no smearing takes place during this period. Meanwhile,
during a period between the time points t11 and t12, the diaphragm
aperture is stopped down according to the aperture value Av2.
During the subsequent period from the time point t13 to the time
point t14, the image condition which is thus acurately exposure
controlled is vertically transferred to the storage part 17. The
image is then read out by means of the shift pulses .0.2 and .0.3
during an ensuing period between the time points t14 and t15.
The level of the output X2 is high during a period from the point
of time t13 to a point of time t16. During this period, the gate
circuit 2 is open to permit a signal, which is read out from the
image sensor 22 and is processed by the signal processing circuit
1, to be recorded by the recorder 3.
In the specific embodiment described, an SPC is employed as the
photometric element 23. However, the invention is not limited to
the use of the SPC. Furthermore, the storing time is controlled by
converging the electric charge at one part within the light
receiving surface to allow it to overflow and by discharging it
into the drain OFD. However, this arrangement may be replaced with
another arrangement in which, for example, each of the picture
elements of the light receiving surface 16 is provided with a drain
via a gate and the storing time is variably controlled by adjusting
a timing at which these gates are opened or closed. Such a method
for variably controlling the storing time is, for example,
disclosed in U.S. Pat. No. 3,944,816.
Furthermore, the image sensor 22 is assumed to be a frame transfer
type CCD for the sake of description. However, the CCD, of course,
may be replaced with some other element capable of performing the
same function.
Furthermore, in the specific embodiment described, the aperture is
adjusted or corrected on the basis of exposure information obtained
with the storing time being controlled. However, it is, of course,
possible to adjust the shutter speed instead of the aperture.
It is also possible to have both the shutter speed and the aperture
value adjusted or corrected.
* * * * *